(i). Field of the Invention
The present invention relates to a redundant information processing system, especially to a redundancy information processing system which comprises three or more processing devices for constituting a redundant system (multiple system) to ensure reliability and in which the processing devices generate control information by performing predetermined information processing based on signals from common signal output means, and control a common object of control with the control information which is determined out of the generated control information by logical decision, for example, majority decision.
(ii). Description of the Related Art
As this kind of information processing system, there is one disclosed, for example, in Japanese Patent Application Laid Open No. 9-134208. This information processing system comprises three controllers as processing devices for independently processing information on their own clock based upon signals from a sensor as common signal output means, and an actuator device with an actuator that is the common object of control in which a combination of a majority decision logic circuit and a control circuit therefore is included.
In this information processing system, the thee controllers perform information processing based on signals from the sensor to generate an actuator control signal. The result of information processing by the controlled is collected and compared in each controller. The results of the comparison in each controller are sent to a storage element of the control circuit in the actuator device. The control circuit decides a normal controller by majority according to comparison result information from each controller. Then, the majority decision logic circuit is activated to selectively transmit an actuator control signal from the normal controller to the actuator. The actuator is thereby operated.
In such conventional information processing systems, however, the control circuit for majority decision and the majority decision logic circuit for selectively allowing the actuator control signals to pass based on the majority decision, which are in the actuator device, are parts each being a single fault point which keeps the actuator from operating when getting into trouble thereof. It has been therefore difficult to ensure sufficient reliability even with the controller part multiplied.
To solve this problem, when the majority decision logic circuit and the control circuit that could become the single fault point are composed of customized parts with higher reliability than that of the parts on the market, the system would cost significantly high. This is especially a crucial point when operation of many actuators needs to be controlled.